1. Field of the Invention
This invention relates to a semiconductor device in which the power source voltage supplied at an external power supply terminal is converted by voltage converting circuits into a predetermined voltage which is to be supplied to an interval circuit. The semiconductor device may be used conveniently with a memory device having a high integration degree.
2. Description of the Prior Art
In a semiconductor integrated circuit device, such as an MOS type device, the tendency is towards smaller size and higher density. On the other hand, as the power source voltage supplied to the circuit device, the voltage having a usual voltage value is used in view of system interfacing and noise margin. If such usual voltage is employed, concentration of the electrical fields or implantation of hot carriers occur within the inside of the integrated circuit device to deteriorate the reliability of the circuit device. Thus it has been proposed to use a voltage which is pulled down from the power supply voltage within the circuit device.
Meanwhile, so-called burn-in is occasionally conducted on the semiconductor integrated circuit device, in which, for the purpose of screening rejects at the initial stage or testing for reliability of newly developed devices, the circuit device is operated under application of a voltage which is higher than the ordinary voltage. In connection with the above described semiconductor integrated circuit device in which the voltage is pulled down within the inside of the device, the following techniques have been known in which the circuit device may be operated positively even when an intentionally high power source voltage is applied thereto for, for example, burn-in testing.
FIG. 1 shows an example of a conventional semiconductor integrated circuit device described in Japanese Patent KOKAI (Laying-Open) Publication No. 63-181196 (1988). With the known circuit device, shown in FIG. 1, the voltage applied to an external power source terminal 3 is pulled down by a supply voltage converting circuit 2 and the thus pulled-down voltage is supplied to an internal circuit 1. The external voltage is directly supplied to an input converting circuit 5 and an output converting circuit 6. When a control signal is supplied from outside to a switching control input terminal 4, a voltage higher than the pulled-down voltage is supplied to the internal circuit 1 to permit reliability tests to be conducted on the circuit device.
However, with the semiconductor integrated circuit device, as shown in FIG. 1, the switching control input terminal 4, which is an extra output terminal, need to be provided in order to carry out the reliability tests. It is however difficult with a complicated multi-function device having a higher integration degree to provide such an extra dedicated external terminal.
FIG. 2 shows another example of a conventional semiconductor circuit device as disclosed in the Japanese Patent Kokai (Laying-Open) Publication No.62-232155 (1987). With the present circuit device, shown in FIG. 2, the voltage supplied to an external power supply terminal 13 is pulled down by a supply voltage converting circuit 12, and the thus pulled-down voltage is supplied to an internal circuit 11. The supply voltage is also supplied directly to an input converting circuit 16 and an output converting circuit 17. During burn-in, a control circuit 14 is activated by a special trigger signal supplied to terminal 13 to fire a MOS transistor 15. As a result, the voltage supplied to terminal 13 is directly supplied to the internal circuit 11 to permit reliability tests, for example, to be conducted on the circuit device.
However, with the semiconductor device, shown in FIG. 2, the external power source terminal 13 need to be supplied with the special trigger signal in order to carry out the reliability tests on the circuit device. In addition, on switching the circuit device, the voltage supplied to the external power source terminal 13 is directly supplied to the internal circuit 11. However, a problem is presented in this case because the supply voltage itself is a sufficiently high voltage. Although a voltage which is not too high so as to be suited to the internal circuit 11 may be supplied during the reliability tests to the external power source terminal 13 in order to avoid an excessively high voltage, the supply voltage would be too low for the input converting circuit 16 or the output converting circuit 17.